Field of the Invention
The present invention relates to a voltage booster circuit, a semiconductor device, and a voltage booster circuit control method.
Description of the Related Art
A voltage booster circuit that boosts and outputs the potential of a predetermined voltage such as a reference voltage or the like is commonly known. In a voltage booster circuit, the boosting of the predetermined voltage is implemented in accordance with a control signal supplied by a booster control circuit (for example, a clock signal or the like). In some cases, the booster control circuit uses a boosted voltage that has been boosted by the voltage booster circuit as a power supply.
This kind of booster control circuit may not start up properly when a power supply to the voltage booster circuit is turned ON.
For example, just after start-up begins when the power supply to the voltage booster circuit is turned ON, boosting is not yet being implemented. Therefore, the boosted voltage is at 0 V. Therefore, the power supply to the booster control circuit is at 0 V, and the booster control circuit cannot start up. Because the booster control circuit does not start up, boosting cannot be implemented by the voltage booster circuit.
Technologies for avoiding this situation in a voltage booster circuit are known. For example, Japanese Patent Application Laid-Open (JP-A) No. H08-185240 discloses a technology that supplies a constant potential from a start-up circuit when oscillation begins in an oscillator circuit that uses a voltage boosted by the voltage booster circuit as a power supply and supplies a clock signal to the voltage booster circuit.
As another example, a voltage booster circuit is known (see FIG. 8, voltage booster circuit 100) in which a reference voltage line and a boosted voltage line are connected by a diode. A reference voltage is supplied through the reference line. The boosted voltage line supplies a boosted voltage that serves as a power supply voltage for a booster circuit control section, which is a booster control circuit. In the voltage booster circuit 100, when the power supply is turned ON, the reference voltage supplied to the reference voltage line is supplied through the boosted voltage line to the booster circuit control section and the booster circuit control section starts up in accordance with the supplied power supply voltage.
However, in the conventional voltage booster circuit 100 described above, because the reference voltage is supplied to the boosted voltage line via the diode, the potential of the power supply voltage supplied by the boosted voltage line suffers a voltage drop due to the diode, and the potential is lowered from the potential of the reference voltage by the forward voltage drop VF of the diode. Because of this voltage drop, there may be a malfunction in the boosting by the booster section. For example, if the reference voltage is a low voltage, the potential of the power supply voltage that is supplied may be lowered by the voltage drop to below a voltage required for start-up of the booster circuit control section, and the booster circuit control section may not start up. As a result, the booster section may not start up.